1. Field of the Invention
The present invention relates to electric connectors used in cables for signal transmission.
2. Description of the Related Art
Electric connecters for use in latest personal computers and the like are required to provide matched impedances and low crosstalk. In this regard, connectors having microstrip line structures have been proposed (see, e.g., Japanese Unexamined Patent Publication No. 05-135826).
In a connector of the above-mentioned conventional example, however, contact portions at leading ends of contacts that are press fitted and fixed in a housing are disposed outside of a dielectric housing and fully exposed to the air; in this respect, the conventional example does not have a microstrip structure in a strict sense, and sufficient impedance matches are not obtained therein.
That is, the press-fitted and fixed portions at the proximal ends of the contacts are covered with plastics material of the housing, while the contact portions at the leading ends of the contacts are surrounded by the air. The air is about one third smaller in permittivity than plastics material. Hence capacitance at the contact portions of the contacts is smaller than that at the press-fitted and fixed portions, resulting in impedance mismatch. Due to this impedance mismatch, the conventional connector is disadvantageous in terms of transmission characteristics.
Particularly, since is it impossible to cover the contact portions of the contacts with plastics material or to remove plastics material surrounding the press fitted and fixed portions. Consequently, impedance matching must be effected through other methods, which raises costs accordingly.